1. Field of the Invention
The present invention relates to a two-dimensional solid-state image sensor which yields a video output fit for a display system employing an interlaced scanning system.
2. Description of the Prior Art
An ordinary TV system uses a 2:1 interlaced scanning system in which one picture frame (each frame period being 1/30 or 1/25 sec) is represented by two fields. In order to make the two-dimensional solid-state image sensor fit for the existing system, it is necessary that the image sensor produces a video output of the type fit for the interlaced scanning system.
To meet such a requirement, in a conventional two-dimensional solid-state image sensor, such as a CCD image sensor of an interline transfer arrangement, information stored in odd number rows of plural optoelectro transducers P.sub.11 to P.sub.mn arranged in a matrix form, for example, as shown in FIG. 1, is transferred via a transfer gate 101 to a vertical transfer path 100 provided for each column and taken out as a video signal of an odd number field via the vertical transfer path 100 and a horizontal transfer path 102. Then, stored information of the optoelectro transducers of the even number rows is transferred via the transfer gate 101 to the vertical transfer path 100 and taken out as a video signal of an even number field via the vertical transfer path 100 and the horizontal transfer path 102. FIG. 2 shows the timing for exposure of the optoelectro transducers of the odd and the even number rows and the timing for vertical transfer of their information. For instance, in the case of the exposure time being 1/30 sec, the exposure periods of the optoelectro transducers of the odd and even number rows are staggered 1/60 sec so that the vertical transfer of information of either one of the odd and even number rows is finished within the exposure time of the other.
Incidentally, there is now a strong demand for obtaining a still picture of a desired frame of a moving picture and, to meet this demand, many of recent video systems are provided with a still picture mechanism for obtaining a still picture. In conventional two-dimensional solid-state image sensors, however, there is a lag in the exposure timing of the odd and even number fields as described above, so that if one frame is formed with two fields by reproducing the odd and even number fields alternately, then misregistration is introduced in the picture in the case of the subject to be televised being a moving one, resulting in the picture flickering and hence becoming unstable. To avoid this, the existing video systems is designed so that when to produce a still picture, only one field is usually reproduced; however, this reduces resolution by half, leading to a defect of degraded picture quality.